In the last ten to fifteen years, installations of computer controlled time division multiplexed flexible switching exchanges throughout telecommunications networks, both private and public, have become typical. This is particularly so in North America. With the more recent advent of deregulation of the telecommunications industry in the United States, manufacture of various telecommunications custom feature apparatus, by various entrepreneurial enterprises, has become common place. Although the principles required to provide many of these features have been the subject matter of a multitude of publications including many patents over the past twenty years or so, it has only been recently that such have amounted to more than paper proposals.
For example, one early suggestion that a store and forward message feature be provided in a telephone system was published in U.S. Pat. No. 3,403,383 on Sept. 24, 1968 by H. G. Kienzle et al. Kienzle et al propose that a digital signal compatible store and forward message module be coupled to serve a digital switching system with digital subscriber stations. Analog subscriber stations would be provided with the same service via an associated analog switching system and a digital/analog interface trunk. Data processing circuits common to both of the switches were to be instrumental in managing the store and forward message feature. However in spite of this and competing proposals of that general time frame, it was not until after 1984 that a telecommunications feature apparatus was manufactured by the assignee for digital signal trunk connection to a TDM PCM PBX.
In the last five years or so, more than one manufacturer has successfully supplied feature apparatus which may be installed in conjunction with almost any telephone switch, in a manner similar to that described in U.S. Pat. No. 4,371,752, issued on Feb. 1, 1983, to G. H. Mathews et al and titled "Electronic Audio Communication System". In this patent, feature apparatus is described as being connectable to a telephone switch by means of telephone lines identical to those used to connect analog telephone sets to the switch. The primary advantage of such an arrangement is that the feature apparatus is very easily connected and operated in combination with many of the telephone switching facilities presently in use.
Other examples of a feature apparatus which are of some interest are so called intercept apparatus. One such apparatus is describe by Weed et al in U.S. Pat. No. 3,867,582 issued on Feb. 18, 1975 and titled "REMOTE CONTROL FOR PRIVATE AUTOMATIC BRANCH TELEPHONE EXCHANGE". A more flexible intercept feature is disclosed in a recent U.S. Pat. No. 4,696,028 issued to S. J. Morganstein et al on Sept. 22, 1987, and titled "PBX Intercept And Caller Interactive Attendant Bypass System". Both of these examples have the advantage of being connectable to almost any telephone system by means of standard analog lines and/or trunks.
In each of these examples, the feature apparatus is of a nature that requires significant space in relation to the associated telephone switching equipment. That is to say that the apparatus stands alone or apart from the telephone switching equipment that it serves. This arrangement may carry advantages in that the switch operator or owner is not constricted to any particular manufacturer or supplier when purchasing a feature apparatus and maintenance service for same. However in relation to PBXs, and in particular PBXs as used by smaller business concerns, persons are likely to find it irksome to commit resources to coordinate equipment of dissimilar manufacture and service requirements. Furthermore, space adequate for the latest PBX technology of a few years ago is often inadequate to accommodate an additional, deemed necessary, feature apparatus.
An alternative arrangement may be that of incorporating a feature apparatus inside the switching equipment. Most features co-act with a call controller in the switching facility, in a manner similar to a service circuit in a typical switching facility. Some well known examples of service circuits are tone signalling receiver/senders, progress tone generators and the like. If a feature apparatus is incorporated at a typical service circuit position in the switching network of a PBX, as for example a PBX of present day manufacture by the assignee, the effect is that of providing at the very least thirty time division multiplexed (TDM) channels of full duplex access to the feature apparatus. Such access is essential for many of the service circuit functions, such as for example the prompt supply of dial tone and the capture of DTMF dialing information. However in smaller PBXs such access capacity is likely to go largely unused in relation to a voice message or automated attendant feature. Such unused capacity would nevertheless have to be purchased at significant cost.
It is an object of the invention to provide for a special or customized feature in a telephone switching exchange without incurring a network cost penalty, and without significantly infringing upon a previously adequate but less than abundant network traffic capacity.
It is also an object of the invention to provide for inclusion of a customized or special feature circuit within an equipment enclosure of a switching facility whereby a power supply resource associated with the switching facility is also committed to supporting the feature circuit.